Homochiral alpha-D- and beta-D-isoxazolidinylthymidines via 1,3-dipolar cycloaddition

The introduction of chiral auxiliaries at the C- or N-atom in starting nitrones has been investigated as a stereoselective synthetic route to heterocyclic nucleoside analogues. The carbohydrate auxiliary at nitrogen atom gave the best results, thus allowing an easy and enantioselective synthesis of isoxazolidinyl thymine 26.